Catalysis of the ageing of alkali cellulose



March 15, 1960 B. LEOPOLD ET Al.

cATALYsIs oF THE AGEING oF ALKALI cELLULosE Filed Sept. 2, 1958 Ema En@ Een Een Eau ation :of ".cellulese.

' l he manufacture of viscosesrayon iploys solutions of cellulose. In order to obtain solutions of'llowenough Vviscosity 'to handle. conveniently," the :mn-

iiiniteci States LCATALYSIS OF AGEING F ALKALI CELLULQSE iBengt Leopold, 'Donald B. Mutton, iand iWilliam R. `Sax- '-ton, Hawkesbury, utario, Canada, assignors to dian `-International 'PaperfCompan Montreak Quebec, vrCanada, a corporation of Canada ApplicationSeptember 2, 1958, 'SerialNa 153,447 efciaima (crass-217) '-ro'f fcellophane, rcellulose ethers, or any .other .cellulosic `products in `the manufacture .of :which alkali :cellulose is 4an'intermediate product.

and :cellophane 'em- 1-lecular weight of `l:the .cellulose f must be yreduced con- Vtsidrrablyffrom its original `:valuezfin the-woo'd, :cottoncor -o'ther 'cellulosic'rna'terial fromfwhich itis obtained. This 'cellulose depolyrnerization is .carried 'out mainly in the `vcase Tof Wood 'during the cooking ofitnewood, the bleach- *ing of lthe pulp, and the ageing .'ofthe alkali cellulose. "Depolymerization S by bleachi-ng is V.expensive to the .pulp -manufacturensince it consumes largeiquantities` of chemicls rwhich fare -not inexpensive Zand .'it 'reduces '-yield. Ageing of Vvalkalicellulose mayfrequire .a considerable klengthfof time and it .is expensive and fineiiicientlforlthe rayon manufacturer to .increase Ithat time. lffth'e .rate for depolymerization n'during fageing :could be .".increased "suliicien'tly, then all or most `of the degradation :now

Vcarried out during the bleachinglz-and ageingstepscould `be 4performed duringtherageing period ialone, .and even the :ageing time could 'be reduced. `Thiswouldenable offcaustic soda as a steepingliquid. To effect necessary :economy it is essential to reuse the caustic steeping'solu- .'tions for treating subsequent 'batches of pulp. `When .the

transition metal catalyst is relatively soluble in the :steeping alkali, variable amounts vofthe catalyst areretained v'by the steeping liquid twhen'separated fromthe .alkali cellulose. This leads to large variations Vin ageingreactivity imparted to the alkali .cellulose ,subsequently Aproduced -A This with :.thetresult that viscosity 4control is zdiflicult. is especially. true in the caseiof cobalt compounds which l aremuch more active catalysts..-than corn-poundsofman- ,ganese .or iron.

` Y. b.. traitent .2,525,824 Patented hier. l5, l96

invention, certain .organic complexes for `chelate com- `pounds fof cobalt are not Vonly .substantially completely insoluble .-inwaterY 'audsteeping fcaustic, :but what is `more important an'dunexpected,thcse complexes fretainthe abilityto cata'lyzetheageing of alkali cellulose. These alkalieinsoluble-complexes vnot only -catalyzefthe fage'ing of alkali cellulose, but they are retained by the alkali cellulose and do not .contaminate thesteeping caustic. Consequently, the .present *invention .makes it possible to eifectively catalyze Vthe `ageing'ofthe'ailkali fcellulese without .contaminating the steeping caustic,thereby'pe r :niitting v`reuse of `the :steeping caustic without lthe `cori- .'cornitant `variations in ageing reactivity which "have `plaguedthe prior art. VSincethe Vsteeping caustic, Vafter `separation .from the vrcellulose, containssubstantially'no catalytic .cobalt complex or chelate compound, Yit'fcan' be reusedpwith 'the next batch of cellulose tow'hich an exact amount .of .catalyst yhave "been :added to produce controlled iageing .of thecellulose. During the research investiga- V`tion whichresulted .in the present invention,`it was 'found that only .certain :organiccomplexes orfchela'te compounds `of cobalt v.are `substantially insoluble in steeping rcaustic andyet' retain the abilitytocatalyze theageing or'depolylmerization-cifalkali cellulose. A

The process of fthe invention provides l greater control over the-:degree of and rate-fof depolymerization. 'This sults finweakened'rayon t'ibenstrength.l

'It is an object ofthe'present inventionltorprovide finprovementszin the depolymeriza'tion ofl cellulose.'l

It isalso an object. ofvthefpresent Ainvention to provide 'an 'improved .process rforzthe `tcontrclled'Jdepolynierizatiom of cellulose-.1in :the -nranufacture of viscose :rayon @and cellophane. It.is:a furtlierobject of the:presentfinventionto provide v organic :coordinate compounds er complexes of cobalt .which are substantially insoluble rin -steeping .-alkfali fand yet .catalyze the tageingof -alkali cellulose, .andwhichido not contaminate. the Ysteeping alkali.

'Theforegoing objects, as wellas others, will .heapparent "to vthose skilled in the art from the-presentia- `scription, taken in Yconjunction with ithe .accompanying vcoordinate diagram "illustrating "the 'effect df 'varying amounts 'df one of ithecobalt complex catalysts 'on'the ageing Vofy 'alkali Acellulose. v ln accordance with *the process of the present invenftion ffordepolymerizing cellulose, -afsmll amountof an ,'alkaliinsoluble fcobalt complex fori-coordinate compound as hereinafter defined fis brou'ghtinto 'F'the 'presence ifof :.cellulose, :such as wood fpulp, fand "steeping :alkali nto catalyze ,cellulose depolynnerization '.:Sinceuch :processes `as the viscose process and the manufacture 'fof :cel- :lulose ethers involve .conversion of wcelluloseinto talkli r cellulose, .usually bysteepingsheets ofcellulose y`in tan aqueous ,caustic .soda solution .containing `from -about .1,7

to 25% of .caustic soda, .itis .desirable forfuseinthat iprocess toaddthecobalt complex catalystto theacellulose prior to the steeping operation. After .the )cellulose .had

'been steeped suiicientlyin ftheralkalito substantiallycon- Wehavediscoveredthatin accordance with .the present cobalt complex is sprayed orstripeld on to the'formd bonds with coordinated groups.

or into the cutter. Alternatively, dilute solutions of the cobalt complexes in an organic liquid, such as chloroform, may be employed. In accordance with another method, the cobalt complex may be formed in situ on the cellulose by adding a soluble salt of cobalt, such as cobalt chloride, with the insolubilizing organic complexing agent, the latter being added in excess of the stoichiometric amount necessary to react with and complex substantially all the cobalt chloride.

Although any amount of cobalt complex catalyst may be added to the cellulose, it is usually necessary to add only .very small amounts, because ofthe high catalytic activity of these complexes. In addition, we have found that increasing the amount of cobalt catalyst added to the cellulose has progressively less eect on the rate of ageing, so that normally there is little additional advantage in adding more than p.p.m. of cobalt on the weight of bone, dry cellulose. Similarly there is no lower limit tothe amount of cobalt catalyst which may be applied tothe cellulose. We have found,however, that the lower the catalyst concentration, the more sensitive is the rate of ageing to small variations in the catalyst concentration. For these reasons, we usually prefer to employ between 0.5 and 3 ppm. of cobalt on the weight of bone dry cellulose. As those skilled in the art will recognize, the optimum amount of catalyst will vary somewhat depending upon the original pulp viscosity and the desired viscosity of the aged alkali cellulose, as well as time and temperature of ageing.

It is well known that cobalt forms coordinatecompounds or complexes with a wide variety of anions and neutral molecules. The essential feature of a coordinated group is that it contains an electron pair which it can `share with the metal ion in the formation of a more or less covalent bond. Cobalt usually has a coordination number of 6 and can thus form 6V essentialiy covalent In the case of simple cobalt salts, the coordinated groups are usually water molecules, 6 in number. The cobalt complexes of the present invention are formed with bifunctional organic reagents which form more than one covalent bond with the cobalt ion. When the positive charges of the cobalt ion have been neutralized by coordinate groups, the resulting complex is electrically neutral and is no longer an electrolyte. These characteristics of the cobalt complexes of the present invention are responsible for their insolubility in water and alkaline solutions.

The cobalt ion is capable of existing in the bivalent or trlvalent state. In its simple salts such as the chloride, thc cobalt is almost always bivalent. Most complexes or coordinated compounds of cobalt usually occur with a trivalent cobalt ion. The cobalt complexes of the present invention appear to occur as mixtures of the complexes formed by bivalent and trivalent cobalt with the organic complexing agent. While no precise valence can be ascribed to the cobalt in the complex, the complexes of the invention may be characterized in terms of their alkali insolubility and from the fact that they are produced by reacting a water-soluble salt of cobalt, such as cobalt chloride, with a stoichiometric excess of the organic complexing agent. K

The cobalt coordinate compounds or complexes suitable for use as catalysts in the invention may be characterized as cobalt ortho-nitroso-substituted naphthols and naphthylamines. Desirably they possess the following structural formula:

Ycomplex with cobalt.

wherein:

n is a number between 2 and 3;

X is a nitroso group;

Y is a hydroxyl group or an amino group; the positions of X and Y are interchangeable.

Examples of the cobalt complexes of the invention are the complexes of cobalt with alpha-nitroso-beta-naphthol, beta-nitroso-alpha-naphthol, and alpha-nitroso-beta-naphthylamine. It is believed that the nitroso group undergoes isomerization to form an oxirne group when forming a Consequently, it is contemplated that exime counterparts of each of the nitroso compounds may be employed in providing complexes. f

In order more clearly to disclose the nature of the present invention, the following examples illustrating the invention are disclosed. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention vnor limit the ambit of the appended claims. In the examples which follow, and throughout the specification, the quantities of materials are expressed in terms of parts by weight, unless otherwise specified, vand cobalt concentrations are expressed in terms of ppm. of cobalt per weight of bonedry cellulose.

EXAMPLE l A web of Kipawa Tenacell tire cord grade of sulphite wood pulp was spotted uniformly with a dilute chloroform solution of the cobalt alpha-nitroso-beta-naphthol complex of Example 5 hereinbelow in sufficient amount to deposit about 3.0 ppm. of cobalt on the puip. The cobalt solution was of such concentration and the pulp was of such thickness and moisture content that about 10 to 15drops of cobalt complex solution were required per square footof pulp. The pulp sheets were then air-dried in an atmosphere of 65% relative humidity. The dried pulp was steeped for 45 minutes at room temperature (22 C.) in the customary manner in a caustic soda steeping liquor containing 216.5 gms. of sodium hydroxide per liter of solution and containing also 5 gms. per liter of hemicellulose. The resulting alkali cellulose sheets were then drained and pressed to expel the steeping liquor to give a cellulose content of 32% The sheets were shredded and the alkali cellulose crumbs were aged for 24 hours at 22 C. The crumbs were then xanthated with 39% of carbon disulde based on the weight of cellulose in the alkali cellulose by reacting for 21A hours at 26 C. in the absence of air. TheV resulting xanthate was then mixed with dilute sodium hydroxide solution to giveV a viscose having a composition of about '7% cellulose and 6% sodium hydroxide. The resulting viscose hadA a lspinning viscosity of 92.4 seconds when measured by the falling ball method. A sample of identical pulp but without the cobalt addition, processed in an analogous manner, required 30% more ageing time to give the same viscose spinning viscosity. The tensile and durability properties of rayon produced from the viscose of the example and of the control were equivalent.

The extent of any contamination of the used steepng caustic by cobalt complex in the example was determined. The caustic drained and pressed from the pulp was reused to steep further batches of control pulp, sucient fresh caustic being added to replace the caustic taken up by the previous batch of cellulose. Control batches of alkali cellulose employing the used caustic were then aged and made into viscose as described and the spinning viscosity measured. It was found that, when caustic from the batch treated with cobalt complex was reused, the spinning viscosity of the second batch of viscose was substantially the same as that obtained when caustic which had at no time been treated with cobalt complex was used for steeping. This indicated that the cobalt complex catalyst was completely retained by the alkali cellulose and none of the complex contaminated the recovered steeping caustic. 'Onthe otherhand, when caustic used to steep a batch of pulp containing the same amount of cobalt inthe ferm of `cobalt chloride was reused, the spinning viscosityof theviscose was'lessth'an half that .obtained whencaustic. from .the above iexample, Iemploying the .cobalt .complex-of zthe invention, ywas reused. This indicated the high degree of contamination of the steeping caustic when employing an alkali soluble cobalt salt, such as cobalt chloride.

EXAMPLE 2 The foregoing example was repeated, except that varying amounts of cobalt alpha-nitroso-beta naphthol complex varying from G to 5.0 p.p.m. :cobalt based upon bone dry pulp was employed, and the resulting alkali cellulose was subjected to various ageing periods of from to 64 hours at 24 C. The degree of polymerization (D.P.) was observed for each of the various amounts of cobalt complex catalyst employed over the various periods of ageing. The results are recorded in Table I below and plotted in the accompanying diagram.

1 Time measured from end of shredding. The'diierences. shown for D.P. at time 0 are due to ageing taking place during shreddmg.

EXAMPLE 3 The procedure of Example l was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt was provided by the cobalt-betanitroso-alpha-naphthol complex of Example 6. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose it was found that the ageing time was reduced by 30%. When tested, it was found that the recovered steeping liquor was substantially free from cobalt contamination.

EXAMPLE 4 The procedure of Example 1 was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt was provided by the cobalt-alphanitroso-beta-naphthylamine complex of Example 7. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose it was found that the ageing time was reduced by 30%. When tested, it was found that the recovered steeping liquor was substantially free from cobalt contamination.

The preparation of the alkali-insoluble cobalt organic complexes employed in the foregoing examples is described in Examples 5-7 which follow:

EXAMPLE 5 COBALT-ALPHA-NITROSO-BETA-NAPHTHOL COMPLEX Alpha-nitroso-beta-naphthol is available commercially. To a solution of 1.0 gm. cobalt chloride hexahydrate in 100 ml. of water was added slowly and with good stirring a solution of 3.0 gm, of alpha-nitroso-betarnaphthol in200 ml.-.of .5.0% sacetic'racid. .The kdarkened precipitate .lteredfo .washed fwithsdilute a'eeticazvmid and water -and dried.

COBALT-BETANITR0so-ALPHANAPHTHoL coMrLEx Beta-nitrosoaalpha-naphthol is available commercially. The preparation of the cobalt complex and its application to the pulp was carried out exactly as described above for the alpha-nitroso-beta-naphthol complex, except that the beta-nitroso-alpha-naphthol was employed.

Y EXAMPLE 7 COBALT-ALPHA-NITRO SO-BETA-NAPHTHYLAMINE COMPLEX Alpha-nitroso-beta-naphthol (15 gm.) was weighed into a thick-walled glass tube and mixed with l5 ml. of 1:1 ammonium hydroxide. The tube was sealed and heated to C. for one hour. After cooling, the tube was opened land the green mass was transferred to a beaker with dilute ammonia, filtered, and washed with more dilute ammonia. The crude nitroso-beta-naphthylamine was dissolved in 1:10 hydrochloric acid and quickly filtered into an excess of dilute ammonia (200 mL). The crystalline material was filtered off, washed with water and recrystallized from aqueous alcohol.

To a solution of 0.5 gm. of cobalt chloride hexahy drate in 5.00 ml. of water was added slowly andwith stirring a solution of 1.5 gm. of alpha-nitroso-beta-naphthylarnine in 1.50 ml. of alcohol. The mixture was boiled for twenty minutes and let standfor another half hour. The precipitate was iiltered olf, washed with dilute hydrochloric acid, dilute sodium hydroxide, and hot water, and then dried.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is: Y

l. In the ageing of alkali cellulose the improvement which comprises catalyzing the ageing of the alkali cellulose with an alkali-insoluble cobalt coordinate compound selected from the class consisting of cobalt orthonitroso-substituted naphthol and naphthylamine complexes.

2. In the viscose process, the improvement which comprises ageing the alkali cellulose in the presence of an alkali-insoluble coordinate compound selected from the class consisting of cobalt ortho-nitroso-substituted naphthol and naphthylamine complexes.

3. In the ageing of alpha cellulose, which comprises ageing alkali cellulose in the presence of an organic cobalt complex having the following structural formula:

wherein n is a number between 2 and 3, X is a nitroso group, Y is a member selected from the class consisting of a hydroxyl group and an amino group, the position of X and Y is interchangeable.

4. The improvement in ageing alkali cellulose which comprises ageing the alkali cellulose in the presence of a complex of cobalt with alpha-nitroso-beta-naphthol.

5. The improvement in ageing alkali cellulosev which I 7 comprises ageing the alkali cellulose in ythe presence of a References Cited in the le' of this patent complex of cobalt with beta-ntroso-alpha-naphthol.

6. The improvement in ageing alkali cellulose which UNITED STATES PATENTS v comprises ageing the alkali cellulose in the presence of 2,682,536 Mitchell June 29, 1954 a complex of cobalt with alpha-nitroso-beta naphthyl- 5 2,768,968 Reppe Oct. 30, 1956 amine. Y l 2,841,579 Villefroy et al. y July 1, 1958 

2. IN THE VISCOSE PROCESS, THE IMPROVEMENT WHICH COMPRISES AGEING THE ALKALI CELLULOSE IN THE PRESENCE OF AN ALKALI-INSOLUUBLE COORDINATE COMPOUND SELECTED FROM THE CLASS CONSISTING OF COBALT ORTHO-NITROSO-SUBSTITUTED NAPHTHOL AND NAPHTHYLAMINE COMPLEXES. 